The present invention relates generally to engine compression release brakes, and more particularly to a system and a method of operating an engine compression release brake.
Vehicle engine compression brakes are conventionally used to assist and supplement wheel brakes when it is desired, for example, to slow heavy vehicles, such as, tractor-trailer trucks. Engine compression brakes are desirable because they help alleviate overheating of the wheel brakes. Engine compression brakes effectively convert an internal combustion engine from a power generating unit to a power consuming air compressor. In engine compression braking systems, it is known that the later the exhaust valve is opened during the compression stroke of the engine cycle, that is, as the piston is disposed closer or closest to the top-dead-center (TDC) position, the more retarding horsepower or braking will be generated or produced. Conversely, the sooner or earlier the exhaust valve is opened during the compression stroke of the engine cycle, that is, as the piston is disposed closer or closest to the bottom-dead-center (BDC) position, the less retarding horsepower or braking will be generated or produced. When maximum engine compression braking is desired, the timed opening of the engine compression brake exhaust valve is such that the engine compression brake exhaust valve undergoes or experiences maximum lift at approximately the top-dead-center (TDC) position of the cylinder piston.
In connection with vehicle engine compression braking schemes, systems, or methods of operating the same, an additional consideration to be taken into account is the duration of the valve dwell of the compression released braking event, that is, the amount of time that the engine compression release exhaust valve is maintained in its opened position. While it has been determined through analysis of various simulations, testing, and the like, that the amount or duration of the valve dwell does not significantly impact upon or influence the amount or level of engine compression braking achieved, the amount or duration of the valve dwell does significantly impact upon or influence the time required to close the compression release exhaust valve and the velocity at which the compression release exhaust valve moves toward its valve seat.
More particularly, the pressure within the cylinder affects the exhaust valve closing time and the velocity at which the exhaust valve seats upon its valve seat. Accordingly, the sooner you close the exhaust valve after the top-dead-center (TDC) position, the higher the pressure within the cylinder and therefore the faster the exhaust valve closes and the greater the velocity at which the exhaust valve seats. If the exhaust valve closes too rapidly, that is, if its seating velocity is too high, damage to the exhaust valve and/or its valve seat can occur. Consequently, a need exists in the art for an engine compression braking or release system, and a method of operating the same, wherein the exhaust valves of the engine cylinders can be activated or energized in various trade-off dwell time modes of operation so as to achieve, on the one hand, the engine exhaust valves must also achieve proper closure time periods and seating velocities.
A still further consideration to be taken into account in connection with vehicle engine compression braking schemes, systems, or methods of operating the same, is the fact that the exhaust valves of the engine also undergo regular or normal cam-driven-exhaust events, and that the compression release or braking event must be conducted or performed, in effect, independently of the normal or regular cam-driven exhaust event such that high velocity impact or interference between the operating or control cam for the normal or regular exhaust event, and the exhaust valve undergoing a compression braking or release event, does not occur, thereby preventing the generation of undesirable noise and potential damage to the engine components. A need therefore exists in the art for an engine compression release or braking system, and a method of operating the same, wherein the dwell of the engine compression release or braking exhaust valve can be appropriately controlled so as to achieve the engine compression or braking mode of operation while avoiding any high velocity interference with or impact upon the normal or regular exhaust valve event driving cam so as to prevent the generation of undesirable noise and potential damage to the engine components.
On such system is disclosed in U.S. Pat. No. 5,357,926 issued on Oct. 25, 1994 to Haoran Hu. In this patent the lash of the engine brake is adjusted to have a clearance between an engine brake slave piston and the engine exhaust valve mechanism. Thus, noise is reduced.
The present invention is directed to overcome one or more of the problems as set forth above.
In one aspect of the invention a method of achieving a compression braking event within an engine which normally has a cam driven exhaust valve event has the steps of providing at least one exhaust valve, having a valve seat, within each one of a plurality of cylinders of a combustion engine, wherein each one of the plurality of cylinders has a piston respectively disposed therein, and wherein the at least one exhaust valve undergoes a crank angle based braking event having a predetermined dwell period, and a crank angle based, cam driven regular exhaust valve event, connecting an electronic control module to each one of the plurality of engine cylinders such that the electronic control module can respectively activate each one of the at least one exhaust valve disposed within each one of the plurality of engine cylinders for performance of the braking event, and programming the electronic control module so as to respectively activate each one of the at least one exhaust valve disposed within each one of the plurality of engine cylinders at a predetermine time during a compression stroke of each one of said pistons respectively disposed within the plurality of cylinders and thereby achieve the braking event, and to variably adjust the dwell period of each one of the at least one exhaust valve as a function of engine speed so as to ensure completion of the braking event prior to commencement of the cam driving regular exhaust valve event.
In another aspect of the invention a system for achieving a compression braking event with an engine which normally has a cam driven exhaust valve event has at least one exhaust valve, having a valve seat, within each one of a plurality of cylinders of a combustion engine, wherein each one of the plurality of cylinders has a piston respectively disposed therein, and wherein the at least one exhaust valve undergoes a crank angle based braking event having a predetermined dwell period, and a crank angle based, cam driven regular exhaust valve event, and an electronic control module is connected to each one of the at least one exhaust valve disposed within each one of said plurality of engine cylinders and is predeterminedly programmed such that said electronic control module can respectively activate each one of the at least one exhaust valve disposed within each one of the plurality of engine cylinders at a predetermined time during a compression stroke of each one of the pistons respectively disposed within the plurality of cylinders and thereby perform the braking event, and to variably adjust the dwell period of each one of the at least one exhaust valve as a function of engine speed so as to ensure completion of the braking event prior to commencement of the cam-driven regular exhaust valve event.